The response of infants and children to first infection with RSV subgroup A or subgroup B respiratory syncytial virus (RSV) was characterized using an ELISA specific for each G glycoprotein. Infection with a subgroup A virus gave a broad response to the G glycoprotein of both A and B viruses, whereas the response to subgroup B virus was predominantly homotypic. Subgroup specific neutralization assays are currently being performed on sera obtained following first and second infections with RSV.